Induction heating



Oct. 3, 1933.

G. D. ONEILL INDUCTIOli HBATIHQ Filed March 4. 1931 Patented Oct. 3 1933INDUCTION HEATING George Dean ONeill, Beverly, Mass, assignor to HygradeSylvania Corporation, Salem, Mass., a corporation of MassachusettsApplication March 4, 1931. Serial N 0. 520,008

13 Claims.

In the art of heat treatment by induction it is often desirable to heatcertain parts without correspondingly heatingan adjacent part or partsbut inasmuch as the induction is effected by core- 5 less coils whosefields spread widely it has not been possible to establish a verydefinite or distinct boundary for the heat zone. For example, in themanufacture of radio tubes and the like containing getters it isdesirable to heat all the metal parts within the tubes during theevacuating process to liberate occluded gases but the getters must bemaintained at a comparatively low temperature until time for flashing;and owing to the close grouping of the parts within the restrictedspaces of the tubes it has been difficult if not impossible adequatelyto heat the electrodes and other metallic parts without prematurelyflashing the getters.

Objects of the present invention are to provide 29 a method andapparatus by which the heat zone may be sharply bounded at least on oneside and/or two juxtaposed parts may be treated effectively whilemaintaining an intermediate part at a comparatively low temperature, toattain these results without insulating barrier-sand generically toimprove the art of heat treatment by vinduction. More particular objectsare to heat interior parts of electron discharge tubes having getterswithout flashingthe getters and at the 30 same time to make the heattreatment thoroughly effective in parts close to the getters.

In one aspect the present invention comprises creating in offset butoverlapping relationship to the usual induction field, a counterfieldwhich varies synchronously therewith so that the two fields tend toneutralize each other in the overlapping zone, whereby heating isinhibited in said zone. In case parts are to be heated on each side ofthe relatively cool zone the counter field may also be utilized forheating purposes by suitably regulating its magnitude and distribution.

In another aspect the invention comprises induction apparatus having thenovel characteristics setforth hereinafter and illustrated by way 45..of example in the accompanying drawing in which:

Fig. 1 is an axial section of a heating coil for heat treatment of radiotubes, a typical tube being shown in elevation with the parts brokenaway;

Fig. 2 is a top plan view of the parts shown in Fig. 1; and

Fig. 3 is a diagram illustrating the theory of? operation.

The particular embodiment of the invention chosen for the purpose ofillustration comprises upper and lower coils C and C' joined together byan intermediate part I. These coils may be of any suitable type as forexample of the type comprising copper tubing flattened so that with agiven spacing between turns more turns may be accommodated within agiven axial dimension. By interconnecting the coils by means of tubingthe cooling water may be circulated through the coils in series, thewater entering or leaving at the lower end A of the lower coil andleaving or entering at the upper end B of the upper coil. The source ofcurrent may also be connected to the ends A and B.

r The particular tubes shown in the figures comprises electrodes andother metallic parts (indicated generally by the reference character D)in the upper part of the tube and a metallic clamp E surrounding thereentrant stem of the tube for supporting certain of the parts D. Agetter-holder is shown at G. From the foregoing it will be understoodthat in the process of evacuating tubes such as shown at 1 it isdesirable to heat the parts D and E to a relatively high temperaturewithout correspondingly heat ing the getter G.

As will be evident from Figs. 1 and 2 the turns of the coils C and Cprogress from top to bottom or vice versa in opposite directions aroundthe common axis of the coils; that is, viewing the coils from the top,the turns of the upper coil C progress from top to bottom in a clockwisedirection and the turns of the lower coil progress from top to bottom ina counterclockwise direc tion. Thus when the coils are operated inseries from the same source the fields inside the res ective coils arealways in opposition as ted in Fig. 3. Consequently, the region betweenthe two coils near the common axis, in which the getter G is located, isrelatively free from heating effects. Thus the parts D and E may beheated to a relatively high temperature without flashing the getter G.

It will of course be understood that this inven tion has many otherapplications than that chosen for the purpose of illustration and thatthe invention as defined by the appended ciaims may be carried out inmany difierent ways. For example the coils may be connected either inseries or in parallel and the turns of the respective coils may progresseither in the same or opposite directions depending upon the manner inwhich the coils are connected to the source or sources of current.

I claim:

1. In the manufacture of radio tubes and the like which contain parts tobe heated by induction during evacuation and a juxtaposed getter which,to avoid flashing during evacuation, must be maintained at acomparatively low temperature, the method which comprises heatingsaidparts by induction with a variable field in the locality of said partsand at the same time creating a counter field in the region of thegetter, whereby heating is inhibited in the getter;

2. The method of localizing heat treatment by induction which comprisescreating a variable field in the desired locality and at the same timecreating in offset but overlapping relationship to said field a counterfield, the two fields varying synchronously and tending to neutralizeeach other in the overlapping zone, whereby heating is inhibited in saidzone.

lhe method of effecting heat treatment in two juxtaposed locations whilemaintaining a comparatively low temperature in the intermedi:- ate zonewhich comprises prmzlucing in said locations opposed synchronous fieldswhich overlap in said zone.

4. Induction heating apparatus comprising coils arranged injuxtaposition so that when energized their fields are in partcoextensive and means for energizing the coils oppositely so that thefields tend to counteract each other in at least a part of theircoextensive zone.

5. Induction heating apparatus comprising approximately coaxial coilsarranged in iuxtaposition so that when energized their fields are inpart coextensive, and means for energizing the coils oppositely so thatthe fields tend to counteract each other in at least a part of theircoextensive zone.

6. Induction heating apparatus comprising coils arrangedend to end sothat when energized their fields are coextensive in a zone therebetween,and means for energizing the coils oppositely so that the fields tend tocounteract each other in said zone.

'7. Induction heating apparatus comprising approximately coaxial coilsarranged end to end so that when energized their fields are coextensivein a zone therebetween, and means for energizing the coils oppositely sothat the fields tend to counteract each other in said zone.

8. Induction heating apparatus comprising coils arranged injuxtaposition so that when energized their fields are in partcoextensive, the coils being connected in series but having their turnsprogressing oppositely so that the fields tend to counteract each otherin at least a part of their coextensive zone.

9. Induction heating apparatus comprising approximately coaxial coilsarranged in juxtaposition so that when energized their fields are inpart coextensive, the coils being connected in series but winding inopposite directions around their common axis so that the fields tend tocounteract each other in at least a part or their coextensive zone.

10. Induction heating apparatus comprising coils arranged end to end sothat when energized their fields are coextensive in a zone therebetween, the coils being connected in series but winding in oppositedirections so that the fields tend to counteract each other in saidzone.

11. Induction heating apparatus comprising approximately coaxial coilsarranged end to end so that when energized their fields are coextensivein a zone therebetween, the coils being connected in series but windingin opposite directions so that the fields tend to counteract each otherin said zone.

12. The method of selectively heating a body by induction whichcomprises subjecting said body to opposed fields which overlap tomaintain a portion of said body comparatively cool, and adjusting themagnitude of one of said fields to control the heating of anotherportion 0! said body.

13. The method of selectively heating a body by induction whichcomprises subjecting said body to opposed fields which overlap to apredetermined extent to maintain a predetermined portion of said bodycomparatively cool, and adjusting the distribution of one of said fieldsto control the heating of another portion of said body.

GEORGE DEAN ONEIIL.

